Power transmisson

[KeithO]

Off grid .

Why do people using wind or hydro usually send power at low voltage , 24v etc using large cables to a battery bank and a inverter near the house instead of putting them near the power source and sending at it at higher voltage using smaller cables to the house?

What am I missing . it must be more than just monitoring

Keith

[mobile_bob]

Keith

i agree with your assessment, if it were me i would generate at as high a voltage as possible, then transport it
as AC, rectify at the house, or as you state put the batteries and inverter closer to the point of generation.

in some cases i might even use step up transformers, depends on the source and the distances involved i suppose.

it seems as though those that transport low voltage DC are limited in funds or are just getting started, maybe?

or maybe they have other concerns? such as safety of lower voltages?

in any event transporting 12/24volts long distances can be very costly in copper or one has to accept some fairly high losses
which usually are significant for alternative power generation sources such as wind and micro hydro.

bob g

[Tom Reed]

Wind is typically sent over the wire as "wild" 3ph AC in a fairly high voltage. The DC converter is usually located near the batteries and dump load. And I don't think there is a typical hydro installation. On our off-grid PV 48 VDC system we have 3 panel series strings to send the DC to the combiner box at 90 VDC and the charge controller steps the voltage down for the batteries.

[sailawayrb]

If you are going any distance and charging batteries, wild high voltage 3-phase AC makes great sense because you minimize wire resistance power loss and turbine speed isn't an issue.

Bob B.

[KeithO]

Cheers guys , what you are all saying about hv wild ac sounds sensible to me .
I'm just not finding too many examples of it poking around the net.
Many just seem use the batteries to clamp the supply to the system voltage
I"ll be using a hydro powered f&p smartdrive hopefully turning at 500rpm so will be looking at 233hz at 250 w , through 100 metres of cable to the house .
Still having said that , putting everything near the generator is still easily done here if the first scheme has issues.
There is also the option of rectifying at the source and using hv dc with a mppt controller at the house.
We shall see when I lash it all together  carefully assemble it


Keith

[rcavictim]

I have a 12 wire, STC 24kW head on my wind turbine and have wired it to produce the highest output voltage in wye config which is ~460 VAC.  I will be running this wild freq and voltage back to the house on overhead aluminum house drop line.  Might be a 500+ foot run.  At the house I plan to use a variable 3-phase motorized variac to stabilize the voltage as much as possible and then power a big 3-phase 400 amp (35 kVA)Hobart welder to be used as a 48 volt battery bank charger.  This is all overkill folks so that nothing can get burnt out.

I still need to come up with a circuit and plan to drive the variac control motor and a MPPT charge controller to drive the SCR's in the Hobart welder.

[KeithO]

RCA
I've seen your pics

You're a braver man than I am, Gunga Din

[rcavictim]

RCA
I've seen your pics

You're a braver man than I am, Gunga Din

Thanx Keith.  I sure bit off a big one.  My health has really deteriorated in the past couple of years and right now with just finishing details, and believe me the devil "IS" in the details, I am trying desperately to get this beast up and running.  I'm presently in the finishing stages of the brake actuator system, right now machining a brake application force transducer from scratch (every single place I look on this machine there is a full sized project right there), and then must get on to finishing my four huge airfoils.  On top of my many sick days the weather has been too nasty to work outside much this year so far as well.

As far as the topic here, I am trying to send as high a voltage as is practical from the generator and the way I'm going will do fine for minimizing losses here.  I am seriously considering removing and bypassing the AVR module that came in my STC-24K so that the alternator will get maximum possible excitation at whatever speed it is turning and will therefore put out the max voltage available at whatever speed it is turning.  Reason for this is my setup is unlikely to get the head up to it's rated 1800 RPM in normal operation.  I'm expecting a lot of operation in the 900 RPM or 30 Hz regieme.  To maximize power here I went with a much larger 60 Hz rated head than I'll ever be able to fully power so as to have enough iron (inductance) in it to give healthy power levels without hitting core saturation at much lower than nameplate speeds.  I expect to be able to pull 12 kW out of this head at just 30 Hz based on my oversize planning.  This 30 Hz and lower regieme explains my acquisition of such a huge welding machine to use as a battery bank charger for the oversized iron transformer in it to avoid saturation issues.

A PM 3-phase slow speed directly driven alternator head may be in the future for this machine if it proves to be successful as presently concocted after it has proven to be reliable enough to warrant some serious investment of coin.  That will be an expensive head!  The advantages are definitely there for a PM head and the efficiency gain by eliminating two gear boxes and a X30 mutiplication ratio between the turbine and the generator head will not be insignificant.  It is all a tradeoff and I just do the best I can with what I have available to work with.  For this project money was not one of the available resources.

[KeithO]

Thanks for the lowdown RCA , it has certainly given me a boost to get my finger out.
Hope your health improves , perhaps you can claim " project fatigue "

Cheers
Keith

[rcavictim]

Thanks for the lowdown RCA , it has certainly given me a boost to get my finger out.
Hope your health improves , perhaps you can claim " project fatigue "

Cheers
Keith

" project fatigue "

Yes, I definitely have a case of that going on now. 

[mobile_bob]

rca

we are all pullin for you man!

this getting older bullcrap is just that,, CRAP!

i am convinced that good health and energy is wasted on youth, at least for me i would have been far better off to have
been a sickly/tired young man and be healthy and full of energy now.

i suspect this is a common problem.

bob g